The present invention relates to a selective sheet feeder, and more particularly to a selective sheet feeder for feeding sheets such as stimulable phosphor sheets selectively into trays or bins according to their size or kind.
There has in recent years been proposed a radiation image recording and reproducing system in which a radiation image of an object can be produced by using a stimulable phosphor. The stimulable phosphor, when exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, stores a part of the energy of the radiation. When the stimulable phosphor exposed to the radiation is exposed to stimulating rays such as visible light, the stimulable phosphor emits light in proportion to the stored energy of the radiation.
The radiation image recording and reproducing system employs such a stimulable phosphor. More specifically, the radiation image of an object such as a human body is stored in a sheet having a layer of stimulable phosphor (hereinafter referred to as a "stimulable phosphor sheet" or a "phosphor sheet"), and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photoelectrically detected and converted to an electric image signal which is processed to reproduce a visible image on a recording medium such as a photographic film material or on a display unit such as a cathode ray tube (CRT). The aforesaid radiation image recording and reproducing system is disclosed in U.S. Pat. No. 4,258,264, for example.
The radiation image recording and reproducing system of the type described above is of greater practical advantage than conventional radiographic systems using a combination of an intensifying screen and an X-ray film in that images can be recorded in a wide range of radiation exposure. More specifically, it is known that the amount of light emitted from a stimulable phosphor upon stimulation thereof is proportional in a highly wide range to the amount of radiation to which the stimulable phosphor has been exposed. Therefore, even if the amount of radiation to which the stimulable phosphor is exposed varies widely under various conditions, radiation images free from such exposure variations can be obtained by selecting a suitable read-out gain in the photoelectric transducer for reading and converting the emitted light into an electric signal, and processing the electric signal into a visible image on a recording medium such as photographic film material or on a display unit such as a CRT.
The radiation image recording and reproducing system is capable of processing a converted electric signal to produce a visible image on a recording medium or a display unit so that the radiation image can well be observed for diagnostic purpose. In this system, the stimulable phosphor sheet does not serve as a final image recording medium, but as a temporary image storage medium for eventually transferring images to the final recording medium or display unit. Therefore, the stimulable phosphor sheet can be used repeatedly, and is economical and convenient if in repetitive use.
To reuse the stimulable phosphor sheet, the remaining radiation energy on the stimulable phosphor sheet after the radiation image has been read out by stimulating rays is discharged by exposure to light, and the stimulable phosphor sheet is employed again for recording a radiation image thereon. The erasure of the radiation energy from the stimulable phosphor sheet is disclosed in U.S. Pat. No. 4,400,619, for example.
The stimulable phosphor sheet which has been exposed to intensive erasing light to erase any remaining image information therefrom may be immediately used for recording another radiation image thereon or may temporarily be stored in a tray or bin in preparation for a next image recording cycle.
Where stimulable phosphor sheets of different sizes and kinds are employed and temporarily stored prior to each image recording cycle, it is preferable that the stimulable phosphor sheets of one size or kind be stored in the same tray. More specifically, stimulable phosphor sheets of different sizes and kinds are normally required to record different zones of an object in different areas as radiation images. In case stimulable phosphor sheets of one size or kind are stored in the same tray, they can quickly and accurately be supplied from the tray for recording next radiation images.
One system for sorting out different sheets includes a plurality of vertically arranged trays which are selectively accessible by a vertically movable device for storing the sheets selectively into the tray according to their size or kind. This sorter is complex in overall construction, and requires a large installation space. Therefore, it is not suitable for use in sorting out stimulable phosphor sheets after image information has been read therefrom upon exposure to stimulating light and any remaining image has been erased therefrom upon exposure to erasing light in a radiation image recording and reproducing system, since the radiation image recording and reproducing system is desired to be composed of unitized components and to be compact in structure. Another problem with this sorter is that its sorting speed is low. After the vertically movable device has received a sheet at a given position, it is moved to a prescribed tray and then delivers the sheet into the tray. Then, the vertically movable device returns to the given position for receiving another sheet. Therefore, the next sheet cannot be fed before the vertically movable device moves back to the given position, with the result that a large time loss is unavoidable in the operation of the sorter.